1. Field of the Invention
The present invention relates to a solvent-soluble aniline conducting polymer, a method for producing the same, a conductive composition with the same, an electric conductor formed from the conductive composition and a method for producing the same. A solution and conductive composition produced from the polymer of the present invention can be applied to various uses for static charging prevention by simple techniques such as coating, spraying, casting, dipping and the like.
The electric conductor of the present invention obtained from the above conductive composition can be used in various uses described below:
Industrial packing materials for semiconductors, electric and electronic parts, etc.; static charging preventing films for recording materials for electrophotography such as films for overhead projectors, slide films, etc.; static charging prevention for magnetic recording tapes such as audio-tapes, video-tapes, tapes for computers, floppy discs, etc.; static charging prevention for the surface of input and display devices such as transparent touch panels, electroluminescence displays, liquid crystal displays and the like; and transparent conductive films or glass used as a transparent electrode, various kinds of sensor, etc.
2. Description of the Related Art
A doped polyaniline (conducting polymer) is well known, but it is insoluble in most solvents, so that it has difficulties in molding and fabricating. A method of polymerizing aniline by electrolytic oxidation [Japanese Patent Application Kokai No. 60-235831; J. Polymer Sci. Polymer Chem. Ed., 26, 1531 (1988)] can form a polyaniline film on an electrode, but it has problems that the isolation of the film is troublesome and also mass synthesis is difficult.
In recent years, there are proposed an alkali-soluble sulfonated polyaniline which develops conductivity without addition of doping agents, its synthesis method, a carboxylated polyaniline and its synthesis method.
For example, the following methods are known as synthesis methods for the sulfonated polyaniline; A method of synthesizing a sulfonated polyaniline electrochemically polymerizing aniline and m-aminobenzenesulfonic acid (Nihon Kagaku-kaishi, 1985, 1124; Japanese Patent Application Kokai No. 02-166165); a method of synthesizing a sulfonated polyaniline by electrochemically polymerizing each alone of o-, m- and p-aminobenzenesulfonic acids [Preprint of the 64th Autumn Annual Meeting of Nihon Kagaku-kai, Vol. II, 706 (1992)]; a method of synthesizing a sulfonated polyaniline by chemically polymerizing aniline and o- and m-aminobenzenesulfonic acids (Japanese Patent Application Kokai No. 01-301714); a method of polymerizing a monomer containing an aminobenzenesulfonic acid compound or that compound and an aniline compound by chemical oxidation (Japanese Patent Application Kokai No. 6-56987); a method of sulfonating with conc. sulfuric acid an emeraldine-type polymer (polyaniline) obtained by chemical or electrochemical polymerization (EP 96319); a method of sulfonating with a sulfuric anhydride/triethyl phosphate complex (Japanese Patent Application Kokai No. 61-197633); a method of sulfonating with a fuming sulfuric acid [J. Am. Chem. Soc., (1991)113, 2665-2671; J. Am. Chem. Soc., (1990)112, 2880; WO91-05979, WO91-06887; Japanese Patent Application Kokai No. 6-145386]; a method of synthesizing an N-substituted sulfonated polyaniline by chemically polymerizing diphenylamine-4-sulfonic acid (sodium salt) [Polymer, (1993)34, 158-162], and the like.
The above method of synthesizing a sulfonated polyaniline by electrochemically polymerizing aniline and m-aminobenzenesulfonic acid (Nihon Kagaku-kaishi, 1985, 1124; Japanese Patent Application Kokai No. 02-166165 and EP-253595) forms a product on an electrode, so that it has problems that an isolation operation is troublesome and also mass synthesis is difficult.
In the above-mentioned Preprint of the 64th Autumn Annual Meeting of Nihon Kagaku-kai, Vol. II, 706 (1992), there is reported a method of synthesizing a soluble conducting polymer by electrolytic oxidation of an aminobenzenesulfonic acid, but it is also difficult to say that this method is suitable for mass synthesis, and further a problem still remains in the performance of the resulting polymer. Also, there is a description that the desired product was not obtained when the chemical oxidation polymerization of an aminobenzenesulfonic acid was carried out with ammonium peroxodisulfate as an oxidizing agent. In J. Am. Chem. Soc., (1991)113, 2665-2671, there is a description that chemical and electrochemical polymerizations of o- and m-aminobenzenesulfonic acids were tried with no success.
In Japanese Patent Application Kokai No. 6-56987, there is a description that a water-soluble conducting polymer is obtained by carrying out the chemical oxidation polymerization of a monomer containing an aminobenzenesulfonic acid compound, or that compound and an aniline compound, in any of acidic, neutral and alkaline solutions.
However, the present inventors' investigation shows that, in order to obtain a polymer having a sufficiently high molecular weight for film formation, it is an essential condition to carry out the polymerization in the presence of a basic compound, and that such a high molecular weight polymer cannot be obtained in acidic and neutral solutions.
In Japanese Patent Application Kokai No. 6-56987, all the examples describe polymerization in a sulfuric acid-containing acidic solution, not in an alkaline solution. Even in examples describing the polymerization in an acidic aqueous solution, there are no data on the molecular weight, so that any physical properties of the polymers obtained are not clear.
Further, the present inventors tried the polymerization in a protonic acid-containing aqueous solution and a simple aqueous solution using ammonium peroxodisulfate as an oxidizing agent. As a result, a water-soluble polymer was obtained, but its molecular weight was so low that such a practical polymer that forms a film was not obtained.
The present inventors traced the method described in Japanese Patent Application Kokai No. 01-301714, wherein aniline and m-aminobenzenesulfonic acid are chemically polymerized using ammonium peroxodisulfate, and the method described in Japanese Patent Application Kokai No. 6-56987, wherein aniline and m-aminobenzenesulfonic acid are chemically polymerized using potassium permanganate. It was found, however, that about only one sulfonic group per five aromatic rings was introduced, and that the resulting polymer showed a high conductivity, but it was completely insoluble in neutral and acidic water and almost insoluble in alkaline aqueous solutions such as aqueous ammonia. Also, when sulfonation is carried out by a method described in Japanese Patent Application Kokai No. 61-197633, about only one sulfonic group per five aromatic rings is introduced as described in page 7 of that literature, because the solubility of polyaniline in a sulfonation solvent is not so sufficient that the reaction is carried out in a dispersion state. The sulfonated polyaniline thus obtained has an introduced sulfonic group at only a low rate and has problems of the conductivity and solubility being not sufficient.
Also, according to J. Am. Chem. Soc., (1991)113, 2665-2671 and J. Am. Chem. Soc., (1990)112, 2800, it is described that when a polyaniline is sulfonated with fuming sulfuric acid, about one sulfonic group per two aromatic rings is introduced. When, however, sufficient sulfonation of polyaniline is tried by this method, a large excess of fuming sulfuric acid is required because the solubility of polyaniline in fuming sulfuric acid is not sufficient. Also, there is a problem that the polymer is easy to solidify when polyaniline is added to fuming sulfuric acid. These problems make a manufacturing process troublesome, and increase the cost of the final product. Further, the polymer and sulfonated product synthesized by the above methods have problems that they are insufficient in conductivity, and that they are soluble in aqueous solutions containing a base (e.g. ammonia, alkylamine), but insoluble in water itself.
According to Polymer (1993)34, 158-162, it is described that when diphenylamine-4-sulfonic acid (sodium salt) is polymerized, an N-substituted sulfonated polyaniline in which one benzenesulfonic group has been introduced into the aniline skeleton is obtained, and that this product is soluble in water itself, but supercentrifugation operation is necessary to isolate the resulting polymer. The present inventors traced this method to find that since this polymer has a high solubility, the yield of the polymer from the polymerization solvent is low, and therefore that when a high-speed centrifugation operation is not applied, the polymer cannot be isolated. Also, it was found that since this polymer is of an N-substituted type, the conductivity of this polymer is low as compared with a polymer synthesized by a method described in J. Am. Chem. Soc., (1991)113, 2665-2671.
Also, a synthesis method for a carboxylated polyaniline is proposed, in which 2- or 3-carboxyaniline or its salt is oxidation polymerized, and the resulting product is treated with a basic substance to obtain the carboxyl group in the form of salt (Japanese Patent Application Kokai No. 4-268331). In this method, the amount of the oxidizing agent required is twice or more by equivalent that of the raw material, and also the value of conductivity is low. This is considered to show that the reactivity of the monomer is low, and therefore a low molecular weight polymer is produced.
Also, a synthetic method is proposed in which methyl anthranilate (anthranilic acid methyl ester) is polymerized in an aqueous acidic solvent in the presence of ammonium peroxodisulfate, and then the methyl ester is saponified with alcoholic potassium hydroxide (Japanese Patent Application Kokai No. 5-226238). This reaction is carried out in two steps, so that operation is very troublesome.
Further, the present inventors tried polymerization of 2-carboxyaniline in a protonic acid-containing aqueous solution using ammonium peroxodisulfate as an oxidizing agent, but the product could not be obtained. Also, the present inventors tried polymerization of aniline and 2-carboxyaniline in a protonic acid-containing aqueous solution using ammonium peroxodisulfate as an oxidizing agent, but the copolymer obtained was low in both solubility and conductivity. This is considered to show that the proportion of copolymerized 2-carboxyaniline in the copolymer obtained is low.
When formability such as film formation by coating is taken into account, in order that coating onto, particularly, any of hydrophilic and hydrophobic base materials may be possible, it is desired to have solubility in both water and organic solvents. However, the sulfonated product of polyaniline has solubility in an alkali water, but it is insoluble in neutral to acidic aqueous solutions, and also its solubility in organic solvents is not sufficient.
As a method to solve these various problems, the present inventors proposed a method for producing the sulfonated product of aniline copolymers characterized in that at least one compound selected from the group consisting of aniline, N-alkylaniline and phenylenediamines is copolymerized with aminobenzenesulfonic acid in acidic solvents using an oxidizing agent, and then the resulting copolymer is sulfonated with a sulfonating agent (DE-4244360). The resulting anilne conducting polymer contains a sulfonic acid group in a rate of 15 to 80% based on the total aromatic rings. However, this method also requires sulfonation operation in conc. sulfuric acid, so that treatment of the waste acid remains as a serious problem. Further, there is a problem of the resulting copolymer being insoluble in water itself.
Any of the copolymers synthesized by the above methods is presumed to have a structure represented by the following formula (9), ##STR1## wherein each of R.sub.11, R.sub.12, R.sub.13 and R.sub.14 is selected from the group consisting of hydrogen and a sulfonic acid group, R.sup.1 is selected from the group consisting of hydrogen and a C.sub.1 -C.sub.4 alkyl group, the rate of sulfonic acid groups is 40 to 80% based on the aromatic ring, X represents a number of from 0 to 1, and n represents a number of from 2 to 1500 showing a polymerization degree.
The polymerization solvent used in the above chemical polymerization is water or aqueous solutions containing a protonic acid. For example, the foregoing Japanese Patent Application Kokai No. 1-163263 describes that when ammonium peroxodisulfate is used as an oxidizing agent, it is desirable to contain a protonic acid having a pKa of, particularly, 3 or less, and that in the polymerization of aniline, those which can dissolve aniline, a protonic acid and oxidizing agent and also are not oxidized by the oxidizing agent are used as a solvent. Also, in Example 3 of the foregoing Japanese Patent Application Kokai No. 4-268331, oxidation polymerization is carried out by dissolving 4 g of sodium anthranilate in 100 ml of water and then adding a solution of 22.7 g of ammonium peroxodisulfate in 100 ml of water to the above aqueous anthranilic acid solution. The pH of this polymerization solvent is also nearly neutral, and it did not occur to anybody from the properties of the polymerization system to positively make alkaline the polymerization solvent and oxidation polymerization system from the standpoint of improvement in the reactivity of the monomer.
A method disclosed in Japanese Patent Application Kokai No. 4-268331 requires a step for treating a product with a basic substance after oxidation polymerization. Japanese Patent Application Kokai No. 6-56987 describes that in polymerization in alkaline systems, an additional acid treatment step is required in order to make the resulting polymer highly conductive. However, the method of the present invention requires such no aftertreatment step, so that there is a merit that the manufacturing process can be reduced by one step.
Examples of the conductive components of the conventional conductive compositions include conducting polymers such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex, polyaniline, etc., those using a metallic powder or carbon powder and a surface active agent, and compositions produced by combining these components and polymer compounds. Examples of the known electric conductors include those formed on a base material using conductive paints comprising the foregoing compositions.
For example, a method of forming metal thin films comprising gold, platinum, etc. and metal oxide thin films comprising indium tin oxide (ITO), etc. on base materials (e.g. plastic film, glass) using an ion beam sputtering apparatus or vacuum deposition apparatus, is known as a method of obtaining electric conductors having excellent transparency and conductivity. However, the apparatus used to form the thin films are expensive, and yet noble metals (e.g. gold, platinum), ITO, etc. used as a material are also expensive, so that there is a problem that the resulting electric conductors become also expensive.
The presently known electron-conductive high-molecular electric conductors with TCNQ include those comprising a polymer compound having a quaternary nitrogen-containing cationic group and TCNQ. These electric conductors are very poor in solubility in solvents, and many of them are soluble only in special solvents such as dimethylformamide, etc. It is therefore difficult to say that these electric conductors are suitable as a varnish.
Conducting polymer compositions comprising a polymer compound and the organic low-molecular complex of TCNQ are proposed (Japanese Patent Application Kokoku No. 44-16499, and Japanese Patent Application Kokai No. 50-123750, No. 54-130651 and No. 1-210470). As to electric conductors obtained by this method, it is thought that the crystals of the TCNQ complex grow in the polymer compound, and that the conductivity of the electric conductors more improves as the degree of overlapping of these crystals becomes larger. However, the state of this crystal growth is easily affected by the rate of volatilization of a solvent and temperature distribution at the time of drying. Therefore, the number of conductive passages per unit area becomes non-uniform to make the dispersion of surface resistance large, so that uniform surface resistance cannot be obtained. Besides, if there is even a slight deterioration of the points of bonding of the crystals in high-temperature conditions (e.g. heating to 140.degree. C.) or high-temperature high-humidity conditions (e.g. 60.degree. C..times.95% RH), there occurs a problem that the number of the conductive passages largely reduces and the conductivity also largely reduces.
A doped polyaniline (conducting polymer) is well known, but it is insoluble in most solvents, so that it has difficulties in molding and fabricating. A method of polymerizing aniline by electrolytic oxidation [Japanese Patent Application Kokai No. 60-235831; J. Polymer Sci. Polymer Chem. Ed., 26, 1531 (1988)] can form a polyaniline film on an electrode, but it has problems that the isolation of the film is troublesome and also mass synthesis is difficult.
On the other hand, there is a report on conductive compositions comprising a polyaniline in an undoped state obtained by chemical oxidation polymerization of aniline and the ammonium salt of a protonic acid having an acid dissociation constant, pKa, of 4.8 or less (Japanese Patent Application Kokai No. 3-285983). However, the polyaniline in the undoped state is soluble only in special solvents such as N-methyl-2-pyrrolidone, so that it is difficult to say that the polyaniline is suitable for a varnish.
Further, the foregoing electric conductor is formed with organic solvents, so that when these solvents are a dangerous substance having properties such as inflammability, explosiveness, etc., there are problems such as safety to working environments and the like. Further, with an increasing interest in safety to human body with respect to the toxicity of solvents and environmental problem on the earth, regulations on various organic solvents exerting adverse effects on human body and environment are being strengthened, so that the safety of conductive compositions is also becoming a serious problem.
In recent years, there are proposed an alkali-soluble sulfonated polyaniline developing conductivity without addition of dopants and its synthesis method, and conductive compositions with it are also reported. For example, conductive compositions comprising the above alkali-soluble sulfonated polyaniline and a polymer compound are reported (U.S. Pat. No. 5,109,70). However, the polymer compound used is poly(1,4-benzamide) resins, polyimide resins, etc. which are extremely low in solubility in organic solvents, and also sulfuric acid, etc. are used as a solvent. Therefore there remains a serious problem in using the compositions as ones for varnish. Also, conductive compositions with such an aniline conducting polymer as described hereinbefore are known. Since, however, the polymer itself has difficult points, use as conductive compositions is also a question.
The electric conductor comprising a carbon powder or metallic powder and a polymer compound is excellent in durability of coating film, but there is a problem that the coating film lacks transparency. Electric conductors are known in which conductivity has been given the surface of their plastic film by kneading a translucent anionic, cationic, nonionic or amphoteric surface active agent into the film, or coating the agent onto the surface of the film, thereby giving hydrophilic property and ionic property. Since, however, the electric conductor obtained by this method is ion-conductive, there are problems that the ion conductivity is subject to the effect of humidity in the atmosphere, and also that conductivity, i.e. the surface resistance per unit area, cannot be made 10.sup.8 .OMEGA./.quadrature. or less.